Multimodal Catheter System and Method for Intravascular Analysis

ABSTRACT

Methods, apparatus, and systems for intravascular analysis combine at least three analytical modalities. In one implementation, intravascular ultrasound, optical coherence tomography, and near infrared spectroscopy are combined to enable detection of multiple, different abnormalities in the arterial morphology during a single intravascular procedure.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.12/437,022 (filed May 7, 2009), which claims the benefit under 35 U.S.C.119(e) of U.S. Provisional Application Ser. No. 61/051,227, filed May 7,2008, the disclosure of which is hereby incorporated by reference.

BACKGROUND

Atherosclerosis is a vascular disease characterized by the modificationof the walls of blood carrying vessels. This modification can take theform of thickening of the vessel wall, eventually forming what arecommonly referred to as “plaques.” The mechanisms corresponding to theformation, progression, stabilization, or rupture of these plaques andtheir effects on humans has been an area of intense research inintravascular medicine. With the advent of interventional cardiology andpercutaneous diagnostic and treatment procedures, the patient withcoronary atherosclerotic disease was no longer required to automaticallysubmit to coronary by-pass surgery—an extremely invasive procedure withattendant risks and extended recovery time. Coronary stents weredeveloped to revascularize narrowed (stenosed) vessels and millions oftheses devices have been placed in patients worldwide. However, currentstatistics show that, while patient comfort and quality of life has beenimproved, treatment of coronary atherosclerotic disease by stenting hasnot significantly reduced the patient mortality. Patients treated withstents are still dying suddenly of heart attack.

Much more is now known about coronary disease than even a decade ago,but there are still many questions to be answered. From retrospectiveautopsy studies on heart attack victims, it has been shown (ref Virmani)that there is often a portion of the coronary artery tree that iscompletely blocked by a thrombosis, or blood clot. The thrombosis istypically in the vicinity of a plaque in the vessel wall. Referred to asthe “culprit lesion,” it would be this blockage that would cut off theblood supply to a portion of the heart, resulting in death of heartmuscle tissue and possibly death of the individual. Certain plaquescontain material which, when it comes into contact with blood, causesthrombogenesis, or clot formation.

These plaques seem to have formed a reservoir, or core, of thrombogenicmaterial behind a layer of fibrous tissue (“cap”), analogous to anabscess. Through some process or set of processes, the integrity of thefibrous layer can become compromised, whereby blood can eventually comeinto contact with the thrombogenic core. This can be a sudden event,where the patient had no prior warning or even symptoms. If onecategorizes plaques broadly as stable—where they may still progressslowly and eventually restrict the vessel—and unstable—those that canchange their status rapidly, among the key questions is: “How can wetell the difference?”

Historically, the search for atherosclerotic disease has been a searchfor the narrowing in the opening or “lumen” of the vessel. Angiographyis one of the oldest intravascular technologies employed for thispurpose. The technique typically employs a catheter, introducedpercutaneously into the vasculature, that is used to inject a contrastagent, consisting of a radio opaque dye, into the blood vessels ofinterest. Using x-rays, a two dimensional live (cine) or still image ofthe vasculature can be obtained. The vessel lumen is visible whereverthe contrast agent is able to flow. From these images, one can determinethe size of the lumen and the presence of any narrowing or blockage. Thepresence of a plaque can sometimes be inferred by a diffuse lumenboundary. Despite being standard of care for many years and forming thebasis for most therapy decisions, angiography alone suffers from somelimitations. First, vessel narrowing is not necessarily rotationallyisotropic. With only a single view angle from which to form the 2-Dimage, areas of narrowing can be underestimated or missed entirely. Toobtain images from multiple viewpoints requires more time and exposureof the patient to contrast and x-rays. The nature of the image as a“lumenogram,” along with limited spatial resolution, make it difficult,if not impossible, to make any statement about the characteristics ofthe tissue in the vessel wall. For example, it is impossible todistinguish between a fibrotic plaque and one with a necrotic, lipidfilled core.

Intravascular ultrasound (IVUS) has emerged, in the last 15 years, as animaging technology to measure tissue structural characteristics, inparticular for blood vessels. IVUS employs a specially designedcatheter, with an acoustic transducer at the distal tip, to send andreceive ultrasonic signals. So called, “mechanical” IVUS cathetersconsist of a flexible polymer outer sheath, inside of which is a corethat rotates and pulls back through the vessel, generating a series ofcircumferential scans of the vessel wall. The core typically consists ofan RF transmission line, connecting the transducer at the distal tip todrive and receive electronics. A helically wound wire cable is typicallyused to transmit torque from a rotary motor, through the core to thedistal tip, to ensure rotation of the tip with consistent angularvelocity. Ultrasonic waves are back scattered by human tissue. Thestrength of the back scatter is a function of tissue properties,including density. The signal returning from tissue from a rotating IVUScatheter can be represented as a radar plot with a 360 degree view of asection of the vessel and the radial dimension showing the strength ofthe signal return as a function of distance from the center of thecatheter. An advantage of IVUS is that it allows one to obtain an imageof the inner walls of the vessel, even through intervening blood. Withaxial image resolution of 100-200 microns and imaging depth of greaterthan 5 mm, various structures within the vessel wall can be visualized,including areas of calcification and thickening of the arterial wall.Also, the boundary between the lumen and the vessel intima as well asthat between the media and the adventitia can be visualized withaccuracy good enough to calculate lumen dimensions and the area ofplaques, or “plaque burden.”

Optical coherence tomography (OCT) is an emerging technology that alsoprovides structural information similar to IVUS. OCT depends on thescattering of light by tissue and uses the coherence properties oflight, for example, using a Michelson interferometer, to determine thedistance at which a scattering event occurred. The technique is similarto IVUS in that a catheter is moved over a guidewire into the bloodvessel to a region of interest and then the core of the catheter ispulled back to scan the artery. However, there are several keydifferences. For example, the OCT signal cannot penetrate blood,requiring that the blood be cleared from the area of the vessel beingimaged. A variety of methods have been employed to accomplish this, themost promising and least dangerous to the patient being a non-occlusiveflush, using a bolus of saline/contrast mix. This method providesseveral seconds in which to obtain an image of a vessel segment.

Another class of intravascular analysis systems uses chemical analysismodalities. These approaches generally rely on optical spectral analysisincluding near infrared (NIR), Raman, and fluorescence spectralanalysis.

Near Infrared Spectroscopy (NIR or NIRS) is a technique, again usinglight in the near infrared region of the spectrum, intended not to imagethe physical structure of the artery, but the chemical constituents,specifically cholesterol, of the arterial wall. Unlike OCT, NIR canperform such measurement through blood. Operation of a NIR catheter isvery similar to that of IVUS with regard to insertion into the patientand pullback and acquisition of data. The result is a two dimensionalmap of the cholesterol, or lipid, content of the artery.

NIRS utilizes an intravascular optical catheter which, similarly toIVUS, is driven by a pullback and rotation unit that simultaneouslyrotates the catheter head around its longitudinal axis while withdrawingthe catheter head through the region of the blood vessel of interest.

During this pullback operation, the spectral response of the innervessel walls is acquired in a raster scan operation. This provides aspatially-resolved spectroscopic analysis of the region of interest. Thestrategy is that by determining the spectroscopic response of bloodvessel walls, the chemical constituents of those blood vessel walls canbe determined by application of chemometric analysis, for example.

In Raman spectral analysis, the inner walls of the blood vessel areilluminated by a narrow band, such as laser, signal. The Raman spectralresponse is then detected. This response is generated by the inelasticcollisions betweens photons and the chemical constituents in the bloodvessel walls. This similarly produces chemical information for thevessel walls.

Hybrid IVUS/optical catheters have been proposed. For example, in U.S.Pat. No. 6,949,072, which in incorporated herein by this reference inits entirety, a “device for vulnerable plaque detection” is disclosed.Specifically, this patent is directed to intravascular probe thatincludes optical waveguides and ports for the near infrared analysis ofthe blood vessel walls while simultaneously including an ultrasoundtransducer in the probe in order to enable IVUS analysis of the bloodvessel walls.

SUMMARY

Aspects of the invention relate to systems, methods, and apparatus forcombining three or more intravascular analysis modalities—and therebyexploiting the different diagnostic information available from eachmodality—in a single intravascular procedure.

Thus, the present invention concerns multimodal intravascular analysis.In one embodiment, a single catheter combines multiple diagnosticmodalities, such as 3, 4 or even 5 diagnostic modalities. In someexamples, two or more of the diagnostic modalities are usedsimultaneously, even during the same pullback and rotation cycle. Inother examples, the modalities are employed serially in separatepullback and rotation cycles.

In general, providing catheter systems that yield chemical information,such as from NIR, Raman, and/or fluorescence spectroscopic analysis,along with other information: lumen dimension (stenosis) and vesseldimension (positive remodeling) and cap thickness (a possible indicatorof plaque vulnerability) from IVUS and OCT and fractional flow rate(FFR) from a flow wire, has the potential to increase the likelihood ofa positive patient outcome.

For example, a catheter that combines NIR, IVUS, OCT and a flow wire,provides the physician with a much more comprehensive data set fromwhich to formulate a therapy decision, including stenting, medicaltherapy, or referral to coronary artery bypass grafting (CABG).

A further consideration is the “fusing” of image data obtained fromdifferent modalities (e.g. angiography, NIR, OCT, IVUS) and the accuratespatial co-registration (longitudinal and rotational) of the images.Having one catheter that incorporates multiple invasive imagingmodalities provides a fixed frame of reference that greatly facilitatesco-registration, especially when the diagnostic modalities are employedduring the same pullback and rotation cycle. Success here is furtherfacilitated by including position detection capabilities in the cathetersuch as sensors that detect externally-generated signals, magneticfields, or emitters that generate externally detected signals.

These and other features, aspects, and advantages of the presentinvention will become apparent to those skilled in the art afterconsidering the following detailed description, appended claims andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIG. 1 is a cross-sectional view of an intravascular probe with aguidewire in a distal end of a catheter;

FIG. 2 is a schematic diagram illustrating the use of the cathetersystem and a system controller, according to the invention; and

FIGS. 3-7 are schematic diagrams illustrating embodiments 1-5 havingdifferent component layouts between the pullback and rotation unit 105and a console 106.

DETAILED DESCRIPTION

While IVUS analysis provides valuable information regarding certainstructural aspects of an arterial wall that enables the practitioner toidentify gross structural abnormalities, such as stenosis and otherforms of remodeling, IVUS suffers from a number of inherent limitationsrelevant to the objective of characterizing plaque composition. For thisreason, efforts to extend the capability of IVUS to actualcharacterization of tissue type (e.g. calcific, fibrotic, necrotic) inan effort to differentiate types of plaques and better inform treatmenthave been largely unsuccessful. Among the inherent limitations of IVUSthat limit its efficacy are that calcified regions block the propagationof IVUS radiation. It is not uncommon for a coronary plaque to becovered with a calcific cap, and therefore, such plaque may goundetected in an IVUS analysis. Also, softer plaques, which oftencontain lipids, are generally hypoechoic. Thus, it is from an absence ofsignal that one must infer the plaque composition. Use of a null signalto infer plaque properties is not ideal and can be subject to errors.

OCT, like IVUS, provides information regarding the structural aspects ofthe arterial wall but has the capability to generate images with up toten times better resolution than IVUS. This now enables thevisualization of structures which cannot be seen with IVUS. Inparticular, the thickness of the fibrous cap covering a plaque with anecrotic core can now be measured with high precision. However, OCToptical signals are severely attenuated by blood and also have limitedpenetration in tissue. Not only does this mean that it is necessary toclear blood from the vessel, as mentioned previously, but the imagingdepth in tissue achievable with OCT is limited to approximately 1 mm.

NIRS, as described above, provides information regarding the chemicalconstitution of the artery to identify the, cholesterol, or lipidscontent of the artery.

The inventors have determined that the combination of at least thesethree diagnostic modalities can significantly enhance the efficacy ofthe intraluminal analysis. For example, by identifying a variety ofarterial abnormalities, such as positive remodeling (best detectable byIVUS), thin caps (best detectable by OCT), and a necrotic core (bestdetectable by spectroscopy, e.g., NIR), the diagnostic accuracy can besignificantly improved. Moreover, by combining at least these threemodalities in a single system, apparatus, and method, these multipleinformational components used in the diagnosis can be obtained in asingle intravascular procedure.

FIG. 1 shows an embodiment of an intravascular catheter system 100 thatcombines multiple diagnostic modalities.

In typical operation, the intravascular catheter 100 is advanced into ablood vessel 18 using a guidewire 108 that is threaded through theguidewire lumen 110.

The catheter system 100 further comprises an inner scanning cathetercore 116 and outer sheath 114. The combination of the scanning cathetercore 116 and sheath 114 enables the inner scanning catheter core 116 andspecifically the catheter tip 112 to perform longitudinal translation(arrow 50) and rotation (arrow 52) while the sheath 114 prevents thismovement from damaging the vessel 18 and specifically walls 104.

The tip 112 of the scanning catheter core 116 is located at the distalend of the catheter 100 and includes an optical bench 118 to transmitand receive light, typically infrared light, and an ultrasoundtransducer system 120 to transmit and receive ultrasound energy.

At least the distal end of the sheath 114 is composed of materials thatare transparent to light, e.g., near infrared, employed by the opticaldiagnostic modalities (e.g., a polymer) and will also propagateultrasound used by IVUS.

The optical bench 118 contains the terminations 122 t, 123 t of at leastone delivery fiber 122 and at least one collection fiber 123, whichextend between the proximal and distal ends of the catheter 100. Light125 propagating through and emitted from the termination 122 t of thedelivery fiber 122 is redirected by a delivery mirror 124 towards thevessel, e.g., arterial, wall 104. A collection mirror 126 redirectslight 127 scattered or reflected from various depths of the arterialwall 104 into a distal end 123 t of the collection fiber 123.

In one implementation, a focusing element serves to collect thediverging optical beam from optical fiber 122 and refocus the beam intothe vessel wall. Suitable focusing elements may include a gradientindexed lens, micro-optical lens, a grating or a curved mirror.

In an alternate implementation, a single fiber or fiber bundle mayfunction as both a delivery and a collection waveguide.

In one implementation, the at least one delivery fiber 122 is a singlemode optical fiber that propagates only a single spatial mode within thefiber at the wavelengths of interest. The collection fiber 123 ismultimode fiber having a core diameter of approximately 60 micrometersor larger, including diameters to about 200 micrometers or larger. Inone embodiment, the single mode delivery fiber is used with lightgenerated by a tunable laser. In this embodiment, the delivery fiber isused to couple light both to the vessel walls 104 and back to theinterferometer for OCT analysis. The large core of the collection fiberand higher numerical aperture improves collection efficiency for NIR,Raman, and/or fluorescence spectroscopic analysis. In an alternateimplementation, other suitable sources of optical radiation, such as asuper luminescent light-emitting diode (“SLED”), may be used instead ofor in addition to the tunable laser.

The ultrasound transducer system 120 includes one or more transducersthat direct ultrasound energy 130 towards the arterial wall 104 andreceive ultrasound energy 132 reflected from the arterial wall 104. Inone embodiment, the ultrasound transducer system is longitudinallyadjacent to the optical bench 118. In an alternate implementation, theultrasound system may be located at substantially the same longitudinalposition as the distal end(s) of the delivering and collection fiber(s),offset from the fiber(s), for example, by 180 degrees. Using timemultiplexing in one implementation, a single ultrasound transducer bothgenerates the transmitted energy 130 and received reflected energy 132into an electrical signal carried on wires 128. For example, during afirst time interval, an electrical signal carried on wires 128 actuatesthe ultrasound transducer 120 to emit a corresponding ultrasound signal130. Then during a second time interval, after the ultrasound signal 130has reflected from the arterial wall 104, the ultrasound transducer 120produces an electrical signal carried on wires 128. This electricalsignal corresponds to the received ultrasound signal 132.

The received signal 132 is used by this IVUS analysis modality todetermine the distance D(wall) between the head or distal end of thescanning catheter 112 and the vessel wall 104 and to determine thephysical morphology, or structure, of the vessel wall itself. Forexample, the received signal 132 may be useful for characterizingatherosclerotic plaques, including plaque volume in the blood vesselwall and also the degree of stenosis of the blood vessels.

In other embodiments, the ultrasound signal is generatedphoto-acoustically by sending a light pulse through optical fiber 122with enough energy to create an acoustic event that is detected by theultrasound transducer system 120.

Between the sheath 114 and the core 116 is a transmission medium 134,such as saline or other fluid, surrounding the ultrasound transducersystem 120 to facilitate acoustic transmission. The transmission medium134 is also selected to be transparent to the near infrared lightemitted from and received by the optical bench 118.

A torque cable 136 is attached to a scanning catheter core 116 andsurrounds the optical fibers 122, 123 and the wires 128. This torquecable 136 transmits the torque from a pullback and rotation systemthrough to the scanning catheter head 112. This feature enables thescanning catheter head 112 to rotate within sheath 114 tocircumferentially scan the arterial wall 104 with light 125 andultrasound energy 130.

In one embodiment, the catheter head 112 comprises an internal element150 of a position detection system. The internal element 150communicates with an external element 152, typically outside thepatient's body, in order to determine the position of the catheter tip112 relative to the external element 152. In one embodiment, theinternal element is a sensor that detects a field, e.g., magnetic,generated by the external element 152. The detected position informationis transmitted on wires 128 and is received by controller 300, as shownin FIG. 2.

In one embodiment, a position detection system developed by MediguideLtd. for guidewires and coronary catheterization devices could be used.The technology provides realtime position information. It uses a smallsensor located in the device that is able to determine its positionwithin a magnetic field created around the patient. In this way,additional position information is available, beyond that which wouldtypically be provided from X-ray angiogram images.

FIG. 2 illustrates an exemplary system for supporting multiplediagnostic catheter functions.

The system generally comprises the catheter 100, a controller 300, and auser interface 320.

In operation, first the guide wire and then the catheter 100 areinserted into the patient 2 via a guide catheter (not shown) alreadyplaced in a peripheral vessel, such as the femoral artery 10. Thecatheter tip 112 is then moved to a desired target region, such as acoronary artery 18 of the heart 16 or the carotid artery 14. This isachieved by moving the catheter 100 up through the aorta 12, riding onthe guidewire 108.

When at the desired site, the pullback and rotation unit 105 is usedboth for the mechanical drive to the scanning catheter 112 and also tocouple optical and electrical signals to and from the catheter 100.Specifically, the pullback and rotation unit 105 drives the scanningcatheter core 116 to rotate and withdraw through the outer sheath 114.An exemplary pullback and rotation unit is disclosed in U.S. pat. appl.Ser. No. 11/875,590, filed on Oct. 19, 2007, entitled Optical CatheterCarriage Interlock System and Method (U.S. Patent Application Pub. No.2008-0097223), which is incorporated herein by this reference in itsentirety. This disclosed pullback and rotation unit shows an opticallayout in which the tunable signal from a tunable laser is coupled ontoa rotating and translating drum via a rotary fiber optical joint (FORJ).Returning NIR signals are detected on the drum. Additional detectors areprovided for common mode rejection of noise generated in the FORJ.

The IVUS subsystem 312 and the optical subsystem 310 are activatedduring each pullback cycle to generate appropriate signals fortransmission through the catheter 100 and receive, detect, preprocessand digitize signals returned from the vessel walls 104. In a preferredembodiment, a tunable laser—or other suitable source of opticalradiation—in the optical subsystem generates a narrowband optical signalthat is wavelength scanned over a range in the NIR, covering one or morespectral bands of interest. The same or a different laser—or othersuitable source of optical radiation—is used to generate signals for OCTanalysis of the vessel walls. At the same time, the IVUS subsystem 312is enabled to simultaneously generate ultrasound images of the vesselwalls 104.

In one embodiment, the returning light is transmitted back downmultimode collection fiber 123 of the catheter 100. The returningradiation is provided to the optical subsystem 310, which can compriseone or multiple optical detectors or spectrometers. Light returning ondelivery fiber 122 is also analyzed, for example in an interferometer,in order to perform OCT analysis.

The optical analysis subsystem 310 collects, preprocesses, digitizes andpasses raw spectral and OCT to the computer 117 for further processing,analysis and display information to the user interface 320.

The IVUS subsystem 312 collects, preprocesses, digitizes and passes theinformation from the ultrasound transducer 120 to the computer 117 forfurther processing, analysis and display formation to the user interface320.

In more detail, the IVUS subsystem 312 comprises the drive electronicsfor driving the ultrasound transducer 120 and analyzing the response ofthe transducer 120 to determine the structural measure of interest in anIVUS-type system.

Generally, the computer 117 receives preprocessed, digitized raw IVUS,OCT and NIR data, performs additional processing, scan conversion anddata registration and presents one or more representations of themorphological and chemical structure of the vessel walls to the operatorvia interface 320, as images and/or data maps. The computer 117 maycombine the structural analysis information from the IVUS subsystem 312with information from the optical analysis subsystem 310. For example,information from both systems is combined into hybrid images displayedto the operator on user interface 320. In further examples, theinformation from the IVUS and/or OCT analysis is used to improve the NIRanalysis as described in U.S. appl. Ser. No. 12/062,188, filed Apr. 3,2008, entitled: System and Method for Intravascular Structural AnalysisCompensation of Chemical Analysis Modality, which is incorporated hereinby this reference in its entirety. The collected spectral response maybe used to determine whether each region of interest of the blood vesselwall 104 comprises a lipid pool or lipid-rich atheroma, a disruptedplaque, a vulnerable plaque or thin-cap fibroatheroma (TCFA), a fibroticlesion, a calcific lesion, and/or normal tissue as described in U.S.Pat. Publ. Nos. US 2004/0024298-A1 and US-2005/0228295-A1, which areincorporated herein by this reference in their entirety.

FIGS. 3-7 illustrate different embodiments of the pullback and rotationunit 105 and a console 106 and how components of the optical subsystem310, IVUS subsystem 312, and computer 117 are distributed between thepullback and rotation unit 105 and console 106.

FIG. 3 illustrates embodiment 1. Like the other embodiments discussedbelow, the proximal portion of the catheter 100 connects or interfaceswith the pullback and rotation unit 105. Specifically, the sheath 114connects to the stationary housing 410 of the unit 105. The core 116connects to a drum unit 408 that drives the rotation of the core 116,see arrow 412, and the longitudinal movement of the core 116 relative tothe sheath 114, see arrow 414.

The drum 408 includes a slip ring/FORJ assembly 420 that coupleselectrical and optical signals between the rotating drum 408 and thestationary components of the console 106. The slip rings support theelectrical connections and the FORT supports one or more opticalconnects across the rotating interface. In more detail, control andcommunication electrical connections 422 are provided between computer117 and the drum, along with data connections 424. Optical connections426 are provided between the drum 408 and an NIR/OCT source andinterferometer unit 428 of the optical subsystem 310. Finally, power isprovided to the drum 408 by a D.C. power supply 430 on connection 432.

The computer 117 also controls the NIR/OCT source and interferometerunit 428 of the console. The power supply 430 powers the NIR/OCT sourceand interferometer unit 428 and the computer 117.

In embodiment 1, the components supporting the OCT analysis are providedin the NIR/OCT source and interferometer unit 428 of the console 106.This includes a tunable laser that tunes the scan band for the NIRanalysis. The light returning on the collection fiber 123 of thecatheter 100 is detected on a detector 442 of the optical subsystem 310on drum 408. The electrical components of the IVUS system are similarlylocated on the drum 408, including the transceiver electronics 440 ofthe IVUS subsystem 312. The data generated by the IVUS analysis and theNIR analysis is transmitted electrically to the computer via the sliprings on connection 424.

The FORJ 420 connects the delivery fiber 122 of the catheter 100 to theOCT source and interferometer 428, which includes reference arm, atunable laser, coupler/beamsplitter and an OCT detector such as abalanced detection system.

In the operation of embodiment 1, optical radiation in the near infrared(NIR) spectral regions is used for both the OCT and NIR analysis, beinggenerated by the tunable laser of unit 428. Exemplary scan bands include1000 to 1450 nanometers (nm) generally, or 1000 nm to 1350 nm, 1150 nmto 1250 nm, 1175 nm to 1280 nm, and 1190 nm to 1250 nm, morespecifically. Other exemplary scan bands include 1660 nm to 1740 nm, and1630 nm to 1800 nm.

FIG. 4 shows embodiment 2, which differs from embodiment 1 in a numberof respects. Specifically, in this embodiment, the IVUS transceiver 440of the IVUS subsystem 312 is located on the console 106. Thus the slipring electrical connections must support the transmission of radiofrequency signals on connection 450 between the transceiver 440 and thedrum 408. As a result, this embodiment would be compatible with thepullback and rotation unit described in incorporated application Ser.No. 12/062,188, with minor modifications to support the RF connectionsfor the IVUS subsystem.

FIG. 5 shows embodiment 3, which differs from embodiment 1 in a numberof respects. In this embodiment, the NIR/OCT source and interferometerunit 428 utilizes a broadband source, instead of the tunable laserembodiment 1. In a preferred embodiment, the source is asuperluminescent light emitting diode (SLED).

Thus, to resolve the NIR spectral response of the vessels, aspectrometer spectrograph/detector system 460 is provided, in theconsole 106, in this example. This configuration of the opticalsubsystem 310 requires a two optical channel FORJ 420, channel 426associated with the delivery fiber 122 and channel 462 associated withthe collection optical fiber 123. Such dual channel FORJ components areoffered, for example, by Princetel, Inc. (product number MS2-155-28).

The spectrograph 460 is preferably a high speed device to support highspeed scanning of the vessel walls at about 300 frames/second,simultaneously with the OCT analysis, in some implementations. In oneembodiment, an InGaAs detector array from Hamamatsu Photonics K.K. isused in combination with a Horiba Jobin Yvon Inc. grating, whichdisperses the spectrum over the detector array.

FIG. 6 shows embodiment 4 which differs from embodiment 3 in that theOCT source is not used for the NIR analysis. Specifically, in thisexample, an NIR SLED optical source 470 in provided on the drum 408.Light from the NIR source is combined with OCT light from the OCT sourceand interferometer unit 428 on a single delivery fiber, in one example,or two delivery fibers are provided in the catheter 100, in anotherexample. Light returning on the collection fiber 123 is coupled off thedrum 408 through a dual channel FORJ 420 to spectrograph 460. Thissystem has advantages in that the source for the OCT and NIR can beindividually optimized for each analysis, possibly operating atdifferent wavelength scan speeds and in different scan bands.

FIG. 7 shows embodiment 5, which is similar to embodiment 4, butincludes the capability for Raman and/or fluorescence analysis.Specifically, it includes a Raman and fluorescence excitation source482. The Raman/fluorescence laser source 482 is a relatively high powerlaser and is usually a single frequency laser or laser with only limitedwavelength scanning. The Raman process is a weak and non-linear process.Thus, high excitation powers are preferably used, but below the damagethreshold for the tissue of the vessel walls 104.

The light from this Raman source 482 is selectively coupled onto thedelivery fiber via optical switch 480. In other examples, a wavelengthmultiplexer is used in place of the switch 482 when the optical bands ofthe OCT and NIR systems 428 do not overlap with the wavelength band ofthe light from the excitation source 482. Thus this embodiment addsRaman and/or fluorescence analysis to NIR and OCT modalities.

Serial/Simultaneous NIR/OCT/IVUS Scanning

Depending on the implementation, the IVUS information and the opticalanalysis information are produced during the same or different scans ofthe scanning catheter 112. For example, in one implementation, theoptical information 410 produced by the NIR and OCT analysis, and IVUSinformation produced by the IVUS analysis, are captured simultaneouslywhile withdrawing and rotating the scanning catheter 112 through theblood vessels 104, in the same pullback cycle of the pullback androtation unit 105. In other implementations, the optical information 410produced by the NIR analysis and IVUS information produced by the IVUSsubsystem are captured during the same pullback and rotation operationsof the scanning catheter 112 but the OCT analysis is performed in itsown dedicated pullback cycle. Then the optical information data setproduced by the NIR analysis and IVUS data set are spatially alignedwith the OCT data set, with respect to each other. This alignmentfurther includes compensation for the offset distance D(offset) betweenthe IVUS transducer 120 and the optical bench 118, see FIG. 1.

In a serial scan implementation protocol, the NIR analysis is firstperformed over the entire length of the artery of interest. Thisleverages an advantage of the NIR analysis: neither occlusion nor asaline flush is necessary since the analysis can be performed throughthe flowing blood. This initial NIR analysis is used to identify regionsof the artery that require further analysis via OCT. Another advantageassociated with serial scanning arises from the fact that the OCTanalysis is typically performed at higher scanning speeds in terms ofthe rotation speed of the catheter and the rate of pullback through theartery. Thus when NIR and OCT are performed during separate scans,optimal speeds can be used for both modalities. Another advantage isthat the OCT is performed only at selected locations and thus the lengthof time and volume of the concomitant saline flush is minimized and keptwithin clinically appropriate limits.

Also, any IVUS scan typically takes longer than the OCT scan since ituses slower rotation speeds and pullback speeds than the OCT. Generally,the OCT scan is completed with about 4-5 seconds, which is the windowprovided by a 20 cc saline flush.

Despite the fact that some implementations employ separate scans for theNIR, OCT and IVUS analyses, the disclosed system provides advantages inthat only a single catheter must be inserted in the patient, decreasingrisk to the patient and lowering the time required for the invasiveportions of the procedure.

A final key consideration in the “fusing” of image data obtained fromdifferent modalities (e.g. angiography, NIR, OCT, IVUS) is the accuratespatial co-registration (longitudinal and rotational) of the images.Having one catheter that incorporates multiple invasive imagingmodalities provides a fixed frame of reference that greatly facilitatesco-registration. This registration is further improved by using theposition detection system including the internal element 150 andexternal element 152.

Thus, exemplary embodiments have been fully described above withreference to the drawing figures. Although the invention has beendescribed based upon these exemplary embodiments, it would be apparentto those of skill in the art that certain modifications, variations, andalternative constructions could be made to the described embodimentswithin the spirit and scope of the invention.

1. An intravascular catheter system comprising: at least one opticalfiber configured to transmit optical radiation between distal andproximal ends thereof, wherein said distal end of said optical fiber isin optical communication with an arterial wall; at least one source ofoptical radiation optically coupled to a portion of said optical fiberand configured to generate optical radiation to be transmitted by saidoptical fiber to the arterial wall; an interferometer optically coupledto a portion of said optical fiber and configured to receive opticalradiation transmitted by said optical fiber from the arterial wall andto provide an interference signal for sub-surface imaging of thearterial wall; an optical processing module optically coupled to aportion of said optical fiber and configured to receive opticalradiation transmitted by said optical fiber from the arterial wall andto provide spectroscopic information about the arterial wall fromdetected intensity of the light collected from the arterial wall; anultrasound transducer configured to transmit ultrasound energy towardthe arterial wall, receive ultrasound energy reflected from the arterialwall, and convert the received ultrasound energy to an electric signal;and an ultrasonic subsystem in communication with said ultrasoundtransducer and configured to generate an ultrasonic image from theelectric signal.
 2. The intravascular catheter system of claim 1,wherein said at least one optical fiber comprises a delivery fiber and acollection fiber and wherein said at least one source is opticallycoupled with a portion of said delivery fiber, said interferometer isoptically coupled to a portion of said delivery fiber and configured toreceive optical radiation transmitted by said delivery fiber from thearterial wall, and said optical processing module is optically coupledto a portion of said collection fiber and configured to receive opticalradiation transmitted by said collection fiber from the arterial wall.3. The intravascular catheter system of claim 2, wherein said deliveryfiber is a single mode optical fiber configured to propagate only asingle spatial mode and said collection fiber comprises a multimodefiber.
 4. The intravascular catheter system of claim 1, furthercomprising at least one reflector configured to redirect opticalradiation from said distal end of said optical fiber toward the arterialwall and to redirect at least a portion of the optical radiation fromthe arterial wall toward said distal end of said fiber.
 5. Theintravascular catheter system of claim 1, wherein said at least oneoptical radiation source comprises one or both of a tunable laser and asuper luminescent light emitting diode.
 6. The intravascular cathetersystem of claim 1, wherein said ultrasound transducer is configured toemploy time multiplexing to both transmit ultrasound energy toward thearterial wall and receive ultrasound energy from the arterial wall. 7.The intravascular catheter system of claim 1, further comprising one ormore wires providing an electrical connection between said ultrasoundtransducer and said ultrasonic subsystem.
 8. The intravascular cathetersystem of claim 1, further comprising an outer sheath covering at leasta portion of said optical fiber.
 9. The intravascular catheter system ofclaim 8, further comprising a guide wire coupled to a portion of saidsheath and configured to guide movement of said sheath and said opticalfiber through an intravascular lumen.
 10. The intravascular cathetersystem of claim 1, further comprising a position detection systemcomprising an internal element configured to be inserted into anintravascular lumen along with said optical fiber and an externalelement disposed outside the intravascular lumen, wherein said internalelement and said external element are configured for communicationtherebetween for locating a position of said internal element relativeto said external element.
 11. The intravascular catheter system of claim1, wherein said at least one optical fiber and said ultrasoundtransducer comprise a catheter core, and wherein said system furthercomprises a torque cable coupled to said catheter core and configured totransmit a rotational force to a distal portion of said catheter core.12. The intravascular catheter system of claim 11, further comprising apullback and rotation unit coupled to said torque cable and configuredto withdraw and rotate said optical fiber and said ultrasound transducerwithin an intravascular lumen.
 13. The intravascular catheter system ofclaim 12, wherein said pullback and rotation unit is further configuredto couple optical signals from the rotating optical fiber to thenon-rotating optical processing module.
 14. The intravascular cathetersystem of claim 1, wherein said ultrasound transducer is distally spacedfrom said distal end of said optical fiber.